docs: def segment_pofiles(configuration, locale):
      """Segment all the pofiles for `locale`.
  
      Returns a set of filenames, all the segment files written.
  
      """
      files_written = set()
      for filename, segments in configuration.segment.items():
          filename = configuration.get_messages_dir(locale) / filename
          files_written.update(segment_pofile(filename, segments))
      return files_written